Method for handling timers after an RLC re-establishment in a wireless comminications system

ABSTRACT

A method for handling timers in a wireless communication system includes starting a Timer_Poll_Periodic timer for a Radio Link Control Acknowledged Mode (RLC AM) entity, performing a re-establishment procedure for the RLC AM entity, and not stopping the Timer_Poll_Periodic timer after re-establishment of the RLC AM entity.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 10/064,747,filed Aug. 13, 2002, which is included in its entirety herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for handling timers in awireless communications system, and more specifically, to a method forhandling a Timer_Poll_Periodic timer after an RLC re-establishment in awireless communications system.

2. Description of the Prior Art

Technological advances have moved hand in hand with more demandingconsumer expectations. Devices that but ten years ago were consideredcutting edge are today obsolete. These consumer demands in themarketplace spur companies towards innovation. The technologicaladvances that result only serve to further raise consumer expectations.Presently, portable wireless devices, such as cellular telephones,personal digital assistants (PDAs), notebook computers, etc., are ahigh-growth market. However, the communications protocols used by thesewireless devices are quite old. Consumers are demanding faster wirelessaccess with greater throughput and flexibility. This has placed pressureupon industry to develop increasingly sophisticated communicationsstandards. The 3rd Generation Partnership Project (3GPP) is an exampleof such a new communications protocol.

Please refer to FIG. 1. FIG. 1 is a simplified block diagram of theprior art communications model. In a typical wireless environment, afirst station 10 is in wireless communications with one or more secondstations 20. The first station 10 is comprised of upper layers 12, aradio link control (RLC) entity 14, and lower layers 16 which are belowthe RLC 14. In the following disclosure, all of the RLC entities areassumed to be RLC acknowledged mode (RLC AM) entities. The upper layers12 can deliver messages to the RLC 14 through service data units (SDUs)13. The SDUs 13 may be of any size, and hold data that the upper layers12 wish delivered to the second station 20. The RLC 14 composes the SDUs13 into one or more protocol data units (PDUs) 15. Each PDU 15 of theRLC 14 is of a fixed size, and is delivered to the lower layers 16. Thelower layers 16 include the physical layer, which is in charge oftransmitting data to the second station 20.

The second station 20 shown has exactly the same basic structure as thefirst station 10. The second station 20 also includes upper layers 22,an RLC 24, and lower layers 26. Just as with the first station 10, thesecond station 20 uses the upper layers 22 to transmit SDUs 23 to theRLC 24, and uses the RLC 24 to transmit PDUs 25 to the lower layers 26.The data transmitted by the first station 10 is received by lower layers26 of the second station 20 and reconstructed into one or more PDUs 25,which are passed up to the RLC 24. The RLC 24 receives the PDUs 25 andfrom them assembles one or more SDUs 23, which are then passed up to theupper layers 22. The upper layers 22, in turn, convert the SDUs 23 backinto messages, which should be identical to the original messages thatwere generated by the first station 10. In communication systems, theterms SDU and PDU have broad meanings. For purposes of the followingdisclosure, the term “SDU” is used to indicate SDUs passed from theupper layers to the RLC, and the term “PDU” should be understood as PDUspassed from the RLC to lower layers.

The 3^(rd) Generation Partnership Project (3GPP) specification 3GPP TS25.322 V3.11.0 “RLC Protocol Specification has defined parameters,variables, timers, control PDUs, etc., for operations of the firststation 10 and the second station 20. According to the specification, insome circumstances, the RLC layers 14 and 24 must be re-established withan RLC re-establishment function, e.g. when starting a reset procedure.However, the specification does not specify how the timers should behandled during re-establishment. Due to this lack of guidelines,potential problems could develop due to the improper use of the timers.

Firstly, please refer to FIG. 2, which is a phase diagram illustrating atransmission window of an RLC AM entity according to the prior art.During normal operation, the RLC AM entity 14 (transmitter) transmitsacknowledged mode data (AMD) PDUs to the RLC AM entity 24 (receiver),and each PDU is marked with a sequence number (SN). The SNs have a fixedbit length of n bits. In the preferred embodiment, the bit length n is12. Hence, the SNs have a range of values from zero to 4095 (2¹²−1). Thephase diagram for SNs can thus be represented by a circle. For thefollowing example, point 30 is the sequentially lowest transmitter PDUSN value waiting for acknowledgment from the receiver in the form of aSTATUS PDU, which contains information on which PDUs have beenacknowledged. In other words, point 30 marks the beginning of thetransmitting window. In this example, assume a window size =X. Point 32marks the highest PDU SN value of an AMD PDU that has been sent so far.Therefore, in order to prevent the transmitting window from filling up,the difference of PDU SN values at point 32 and point 30 has to be lessthan X. Otherwise, the transmitting window fills up, and deadlockoccurs. Deadlock can occur if AMD PDUs sent from the transmitter to thereceiver are not properly acknowledged by the receiver. This would causepoint 30 to remain stationary, and the difference between point 32 andpoint 30 would eventually equal the maximum window size of X.

As mentioned in the specification 3GPP TS 25.322 V3.11.0, aTimer_Poll_Periodic timer is started for the RLC AM entity 14 of thefirst station 10 when the RLC AM entity 14 is created, and is used bythe RLC AM entity 14 to poll its peer RLC AM entity 24 to send a STATUSPDU. When the Timer_Poll_Periodic timer of the RLC AM entity 14 expires,a poll request is send to the RLC AM entity 24 asking for a STATUS PDUto be sent back to the RLC AM entity 14. Since the specification doesnot specify how the Timer_Poll_Periodic timer should be handled duringre-establishment, the Timer_Poll_Periodic timer may be stopped by theRLC entity upon reception of a re-establishment request, and neverrestarted after the re-establishment procedure. Therefore, theTimer_Poll_Periodic timer does not ever get started again, and cannottrigger a poll to the peer RLC AM entity 24 upon expiration of thetimer. This means that AMD PDUs with lower SN values indicated by point30 in FIG. 2 will never be acknowledged. Since point 30 never moves,eventually the difference between point 32 and point 30 will equal thetransmission window size of X. Thus, because the timer remains stopped,deadlock occurs, and the RLC AM entity 14 cannot transmit additionalPDUs to the peer RLC AM entity 24.

Therefore, since the current 3GPP specification does not specify howeach of the previously mentioned timers should be handled duringre-establishment, deadlock can occur and quality of service may bereduced substantially.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the claimed invention to providea method for handling timers after an RLC re-establishment in a wirelesscommunications system in order to solve the above-mentioned problems.

According to the claimed invention, a method for handling timers in awireless communication system includes starting a Timer_Poll_Periodictimer for a Radio Link Control Acknowledged Mode (RLC AM) entity,performing a re-establishment procedure for the RLC AM entity, and notstopping the Timer_Poll_Periodic timer after re-establishment of the RLCAM entity.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of the prior art communicationsmodel.

FIG. 2 is a phase diagram illustrating a transmission window of an RLCAM entity according to the prior art.

FIGS. 3 and 4 are message sequence charts illustrating handling of theTimer_Poll_Periodic timer during a re-establishment function accordingto the present invention.

DETAILED DESCRIPTION

Please refer to FIGS. 3 and 4. FIGS. 3 and 4 are message sequence chartsillustrating handling of the Timer_Poll_Periodic timer during are-establishment function according to the present invention. After theRLC AM entity 14 is re-established by upper layers, the presentinvention method includes not stopping the Timer_Poll_Periodic timer.Alternately, as shown in FIG. 4, the present invention method includesrestarting the Timer_Poll_Periodic timer.

Thus, for a re-establishment function, the handling of theTimer_Poll_Periodic timer can be summarized as follows: afterre-establishment, the Timer_Poll_Periodic timer is not stopped or isrestarted. By not stopping or restarting the Timer_Poll_Periodic timer,the RLC AM entity 1 4 will continue to be able to poll its peer RLC AMentity 24 now that the RLC AM entity 1 4 has been re-established, andwill prevent deadlock from occurring.

Compared to the prior art, the present invention provides steps forhandling the Timer_Poll_Periodic timer after re-establishment. Thus,using the method specified in the present invention will prevent RLC AMentities from experiencing deadlock, and will help maintain the qualityof service.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for handling timers in a wireless communications system, themethod comprising: starting a Timer_Poll_Periodic timer for a Radio LinkControl Acknowledged Mode (RLC AM) entity; performing a re-establishmentprocedure for the RLC AM entity; not stopping the Timer_Poll_Periodictimer after re-establishment of the RLC AM entity; and maintaining avalue of the Timer_Poll_Periodic timer and maintaining operation of theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.2. The method of claim 1 further comprising restarting theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.3. A method for handling timers in a wireless communications system, themethod comprising: starting a Timer_Poll_Periodic timer for a Radio LinkControl Acknowledged Mode (RLC AM) entity; performing a re-establishmentprocedure for the RLC AM entity; not stopping the Timer_Poll_Periodictimer after re-establishment of the RLC AM entity for preventingdeadlock from occurring; and maintaining a value of theTimer_Poll_Periodic timer and maintaining operation of theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.4. The method of claim 3 further comprising restarting theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.5. A method for handling timers in a wireless communications system, themethod comprising: starting a Timer_Poll_Periodic timer for a Radio LinkControl Acknowledged Mode (RLC AM) entity; performing a re-establishmentprocedure for the RLC AM entity; not stopping the Timer_Poll_Periodictimer after re-establishment of the RLC AM entity for continuing to polla peer RLC AM entity when the RLC AM entity has been re-established forpreventing deadlock from occurring; and maintaining a value of theTimer_Poll_Periodic timer and maintaining operation of theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.6. The method of claim 5 further comprising restarting theTimer_Poll_Periodic timer after re-establishment of the RLC AM entity.